Hot end coating device

ABSTRACT

The coating method comprises introducing a coating material into an air stream above the pyrolysis temperature of the coating material and directing the air stream at the vitreous surface. The vitreous surface is at a temperature above the pyrolysis temperature of the selected coating material. The apparatus includes an electrical filament heated to a temperature from about 500*F to about 2,000*F. A source of air is blown over the electrical filament and heated to a temperature of from about 400*F to about 1,800*F. The coating material is introduced into the air stream which is then directed at the vitreous surface.

United States Patent 1191 Novice 5] Jan. 15, 1974 HOT END COATING DEVICE1,931,380 10/1933 Haber 117/106 R Inventor: Michael A. Novice, m N.Y.2,375,482 5/1945 Lyle 117/106 R OTHER PUBLICATIONS [73] Asslgnee' gggLos Angeles Vapor Plating by Powell, Campbell & Gonser. John Wiley &Sons 1955 pgs 26-28. [22] Filed: July 1, 1971 I Prima Examiner-MurraKatz 7 '3 y [2]] Appl) No 51 Assistant ExaminerM. SafocleousAttorneyKenneth J. Hovet, Leigh B. Taylor and Paul [52] [1.8. CI 117/54,117/94, 117/105, I R Wyli l17/105.1,117/106R,1l7/l07.2 R, 117/124 A,117/124 T, 117/124 B; 117/124 C, 57 T T 117/211 117/D1G.2 The coatmgmethod comprlses introducing a coating Al material into an air streamabove the pyrolysis temperv Iei l77l0;a|;c07...2...l...l54 {24-1 124ature of the coating material and directing the air 6 54 stream at thevitreous surface. The vitreous surface is at-a temperature above thepyrolysis temperature of the selected coating material. The apparatusincludes an [56] Reterences Cited electrical filament heated to atemperature from about UNITED STATES PATENTS 500F to about 2,000F. Asource of air is blown over 2.877.138 3/1959 Vodonik 117/124 B theelectrical filament and heated to a temperature of 2,065,218 l2/l936Garesche l from about 400F to about 1,800F. The coating mateg y 1 7 92rial is introduced into the air stieam which is then dieyrup 1 2,505,5304/1950 Davis 117/1051 acted at the vmeous surface 3,381,023 4/1968Whiting 117/107.2 R 5 Claims, 5 Drawing Figures /5 A? 2/ U 4 3 l5 1 Z2.1; 1 Q j/ j} /0 PATENIEDJANWW 3.785.851

' sum 2 or 2 7174M di ATTORNEY HOT END COATING DEVICE BACKGROUND OF THEINVENTION 1. Field of the Invention This invention relates to a processfor treating vitreous surfaces such as glass to enhance and alter theproperties. In a more specific aspect the invention relates toa methodfor coating and treating glass containers.

2. Description of Prior Art In the prior art coatings have been appliedto surfaces, particularly vitreous surfaces such as glass, for variouspurposes. Some of the purposes for which coatings have been applied toglass are: to promote adhesion between the glass and another substance,to color the glass or facilitate the acceptance of color by the glass,to improve the abrasion or scratch resistance of the glass, to controlthe reflectance of the glass, to control the wetting properties of theglass, to facilitate the formation of mirrors, to form an electricallyconducting surface on the glass, and to increase the strength,durability and corrosion resistance of the glass.

Glass derives its strength from an unblemished surface and any scratchesor flaws which are present on its surface decreases its strength manyfold. Generally, glass articles of commerce have their maximum strengthas soon as they are formed and this strength decreases as the articlescome into contact with each other, and with other surfaces.

One reason for coating a glass surface is therefore to provide goodscratch resistance or abrasion resistance which decreases the likelihoodof breakage. More bottles can therefore be handled by filling andpackaging apparatus in the same amount of time merely by spacing thebottles closer together and increasing the speed of the conveyors, eventhough the glass surfaces will be subject to more contact with othersurfaces. Also since many products are packaged under pressure, forexample, carbonated beverages, it is very desirable that the surface ofthe glass container have as few scratches as possible to minimize thepossibility of breakage.

Another reason for coating glass surfaces is to provide on the glass orother electrically non-conductive surface a thin transparent coating orfilm possessing the property of electrical conductivity, which coatingsare clear, hard and tenacious and of uniform thickness; which are inintimate contact with the glass or other surface; and which will retainthese properties under adverse conditions.

An electrically conducting coating or glass may be employed for avariety of purposes such as, making burglar alarms, heating elements,electrical resistors and semi-conductors. A special use is theapplication of the conducting glass for glazing the Windshields inairplanes and other aircraft, although it may be advantageously employedfor glazing windows whenever clear vision is required under adverseweather conditions.

Glass surface are also coated togive color to glass. For example, by theuse of coloring oxides corresponding shades 'of a permanent characterare imparted to glass fibers. By the use of various combinations ofcoloringoxides, different shades and color blends may be obtained. Whenthereaction between the metal oxides and glasssurfaces leaves asubstantially colorless product, permanent color can still be developed,because it appears that the resulting surfaces provide sufficientphysical anchorage for conventional coloring agents,

such as dyes, which may then be applied by techniques common in thetextile trade.

Coatings upon glass are used to improve the adhesion of glass tomaterials such as polymers. For example, a metal compound may be coatedupon the exterior surface of a glass container and thereafter thesurface may be coated with a cured resinous composition. The metalcompound acts as an anchoring or bonding agent between the exteriorsurface of the container and subsequently applied resin coatings; andthe cured coating provides a mar resistant, inert film over the bottleexterior While not wishing to be bound by any particular theory it isbelieved that there is present on the bottle surface OH or ONa groups;and that these groups dissociate from the glass when contacted withwater which has permeated an organic, resinous film on the bottlesurface causing the film to lose its adhesion to the surface. During thedeposition of the metal compound on the container exterior, thepotentially dissociable groups thereon are removed or inactivated insome manner.

The metal compound forms on and adheres to the glass surface in amultitude of connected, tiny nodules. These nodules are not hydrophilicbut organophilic and provide anchoring areas to which the subsequentlyapplied organic resin coating can firmly attach itself.

Coatings have been formed using metallic compounds which are highreflecting and, in addition, evenly wettable with water in the firstinstance but nonwettable after washing and drying.

Because of these characteristics, such films are readily adaptable to alarge number of uses. They can be applied to opaque glass to producevery desirable nonglass rear vision mirrors for automobiles. When formedon transparent glass surfaces, a transparent or one-way mirror results,and on transparent glass tableware, they serve to enhance both thebeauty and utility of the pieces. Since the film can uniformly wet withwater, on the first application after fliming, they are valuable as anintermediate coating in silvering, and because of their subsequentnon-wettability they are useful on windows to improve the ability of theglass to shed water and on outdoor insulators to prevent the formationof electric ally conducting moisture films.

The following metals or their compounds have been used for one or moreof the above reasons: aluminum, antinomy, arsenic, barium, beryllium,bismuth, boron, cadmium, calcium, chronium, cobalt, columbium, copper,gallium, germanium, gold, indium, iron, lead, molybdenum, magnesium,manganese, mercury, nickel, phosphorous platinum, potassium, selenium,silicon, silver, sodium, strontium, sulfur, thallium, tellurium,thorium, tin, titanium, tungsten, uranium, vanadium, zinc and zirconium.

Although it is known in the art that the above elements or theircompound can be used for one or more of the above reasons, the method ofapplication known in the prior art are often insufficient.

The most common method of applying a metallic compound to the surface ofa vitreous substance is to spray a metal containing compound or solutionor an emulsion of a metal containing compound onto the vitreous surfacewhile the surface is hot. The spray method of application generallycauses stresses in the vitreous substance, creates a coating which isnot uniform and which has lower scratch resistance than coating appliedby other methods.

It has been proposed that a metal containing compound could be sprayedonto the glass surface at the cold end of the glass forming line. Thismethod of application is inadequate as the sole method for applying ametal containing compound to a vitreous article such as a glass bottle.It is necessary that the article such as a glass bottle be protectedthroughout the processing of the article. A coating applied at the coldend of the processing line will provide no protection for the bottleduring processing. And stresses resulting from coating solely at thecold end will not be reduced by upstream annealing.

It has been suggested that the surface of glass could be coated withcolloidal metal containing compounds. The glass would then be heated sothe colloidal compound would combine with the glass surface. This methodof applying a coating to glass has proven to be deficient in thatnon-uniform uneven coatings are obtained.

In the prior art, attempts were made to coat glass by immersing the warmglass article in a liquid containing metal or a metal containingcompound. Immersing of a warm or hot vitreous substance such as glass ina liquid can cause stresses and in addition coatings formed by immersingan article in the liquid were not uniform.

The method which provides the most uniform coating on a vitreous surfaceinvolves exposing the vitreous substance such as glass to a vapor of ametal containing compound. Vapors cannot easily be applied in open airto the surface of a glass article since loss of vapor to the atmosphereis expensive and since there is a complete lack of control of vaporconcentration. Furthermore, vented metallic vapors are consideredpollutants. In the prior art, it was necessary that the vapors beapplied in an enclosed chamber and the use of the enclosed chamber wasnot suitable for continuous operation since batch processing slowedproduction and jamming occurred in the hood when attempts were made toconvey the article through the chambers. Even in an enclosed chamberconcentration control was difficult. One of the major disadvantages ofusing the vapor method of applying a coating to. a vitreous surface isthat there is a lack of directional control, furthermore, a high scratchresistance is not easily provided by a coating applied by a vapor methodwithout giving a highly reflective unaesthetic appearance to the surfaceof the bottle.

There is disclosed in the prior art, a method for applying a coating toa bottle by including metallic compounds in a combustible organic fluidin the presence of oxygen and directing the mixture at the hot bottle orother vitreous surface which then causes the combustible organic fluidto burn. The method disclosed was not suitable since frequently metallicoxide residue is formed upon the surface of the glass seemingly due toreaction of the metal with water formed by combustion of the organicfluid.

Furthermore, equipment frequently became clogged due to the reactionproduct of hydrolysis of the metallic compound with the water fromcombustion. These reaction products are also believed responsible forrough cloudy coatings. Efficiency of these prior art methods was low andhigh percentages of metallic vapors was wasted. I

The flame type and other prior art hot end coating devices had evenlower efficiencies when compounds duced into the flame, or other coatingmeans in the solid or liquid phase. For these reasons, many compoundscould not be efiectively used commercially. For example, tintetrachloride vaporized at a lower temperature than titaniumtetrachloride and was somewhat less susceptable to rapid hydrolysis thantitanium tetrachloride. Titanium tetrachloride was therefore notgenerally used commercially even though titanium tetrachloride causesless corrosion of metallic surfaces in contact with the coating, iseasier to scrub out of waste gases to prevent pollution, and is acheaper compound. Tin coatings on the other hand causes corrosion ofbottle caps in contact with the coating resulting in pock marks andtwist off" caps which could not be twisted off. The tin tetrachloridewas more expensive than titanium tetrachloride and it was harder to freethe waste gases from tin compounds.

BRIEF DESCRIPTION OF THE INVENTION The method for coating vitreoussurfaces herein disclosed eliminated the problem of articles jamming inthe coating hoods, reduces stresses in the vitreous article, gives acoated surface having high scratch resis- 1 tance, permits the formationof a uniform coating, gives good directional control of the coatingmaterial, permits easy control of the concentration of coating material,permits the more efficient use of coating compounds than was possibleusing prior art methods, and reduces or eliminates troublesomehydrolysis products. These articles may be glass containers, glasssheets, ceramic articles or any other article having a vitreous surface.

Many of the above advantages were accomplished by means of the flamecoating method; however, as discussed above trouble resulted from thecombustion products of the flame. The present method retains all of theadvantages of the flame method while eliminating problems resulting fromcombustion.

In accordance with this invention, a compound containing an elementselected from the group consisting of aluminum, antimony, arsenic,barium, beryllium, bismuth, boron, cadmium, calcium, chromium, cobalt,columbium, copper, gallium, germanium, gold, indium, iron, lead,molybdenum, magnesium, manganese, mercury, nickel, phosphorous,platinum, potassium, selenium, silicon, silver, sodium, strontium,sulfur, thallium, tellurium, thorium, tin, titanium, tungsten, uranium,vanadium, zinc and zirconium, is introduced into an air stream which ispreferably at a temperature above the pyrolysis or decompositiontemperature of the compound, and the air stream is then directed at thevitreous surface to be coated. The compound or coating material isgenerally selected from Fe Cl Ti C1 and Sn Cl, and Ti Cl or Sn Cl havebeen found to be preferred. The vitreous surface to be coated is alsopreferably above the pyrolysis temperature of the selected compound.

The air is dry and may be heated by any means which will raise thetemperature above the pyrolysis temperature of the selected compoundwithout introducing foreign material such as water vapor into the air.The air is preferably heated by an electrical resistance heater althoughit may also be heated by other means such as an electrical are or byheat from a separated IN THE DRAWINGS FIG. I is a front perspective viewof a preferred embodiment of the coating device.

FIG. 2 is a cross sectional view of the gun portion of 5 the coatingdevice. 7

FIG. 3 is a top view of the device shown in FIG. 1. FIG. 4 is a crosssectional view of the tank shown in FIG. 1.

FIG. 5 is an alternative embodiment of the coating.

device having two coating guns.

PREFERRED EMBODIMENT tween 700 and 1,800F and the surface to be coatedshould be at a temperature of from about 400F to about 1,800F. Othertemperature ranges may be required for other coating materials. The airis preferably heated by an electrical resistance heater similar to theSylvania Serpentine Heater which has a heat transfer efficiency of about90 percent.

The coating material is generally introduced into the hot air stream bymeans of a feed air stream carrying the coating material. The coatingmaterial may be in a powder or liquid form but is preferably in thevapor phase.

Referring now to the drawings, FIGS. 1 and 3 show a preferred embodimentof coating apparatus 10. Apparatus is provided with a conveyor 12 formoving article 11 which may be a bottle into a position'to permitarticle 11 to be coated. Gun 13 is aimed at article 11 and spray article11 with coating material. As best seen in FIG. 2, gun I3 is connected toan air hose 19 by means of air hose coupling 21.

Gun 13 is further provided with a heating filament 15 to which areattached heater wires 18. Filament 15 is preferably manufactured from ahigh temperature ferrous alloy or tungsten and may be heated byelectricity up totemperatures of over 2,000F. The filament is preferablyhelical in shape and the helical turns vary in diameter along the lengthof the filament to increase the efficiency of heat transfer to gasespassing over the filament. An example of such a filament is the SylvaniaSerpentine coil available from Sylvanias Emmissive Products. Thefilaments will have a life of over 5,000 hours at a filament temperatureof over 1,900F. Filament 15 in the preferred embodiment is surrounded byquartz tube which is open at both ends 56 and 57. In operation airpassing through the quartz tube receives heat from the filament. Whenthe filament is heated to I,900F, gas passing through the tube willreach temperatures as high as I,700F and when the filament reaches2,000F the gas temperature will reach 1,800F. The temperature of the gasleaving the quartz tube will however drop rapidly as the heated gasstream passes through surrounding air at normal room temperature. At adistance of only seven inches from the to air hose coupling 21. Quartztube 25 is supported within quartz tube shield 26 in a spacedrelationship to shield 26 by means of supports 16 and insulation 24.Insulation 24 also prevents loss of efficiency by loss of heat throughthe sides of quartz tube 25. At end 57 of tube 25, a nozzle 14 isprovided having a feed line cou' pling 23 which connects feed line 22 tonozzle 14. Feed line 22 carried coating material to nozzle 14.

Surrounding quartz tube shield 26 and in spaced relationship thereto isouter cylindrical shell 29 which further assists in preventing heat lossfrom quartz tube 25 through the walls of the tube. Surrounding andprotecting end 56 of quartz tube 25 is outer housing 20 which alsopermits the gun to be manually handled during operation without burningthe operators hands.

As seen in FIG. 1, the electrical and air supplies for gun 13 iscontrolled by control unit 17 which is provided with necessary switchesand controls for regulating the fiow of current through heater wires 18to filament [5 and for controlling and monitoring the flow of air frommain air supply hose 46 through quartz tube 25. In operation air frommain air supply hose 46 enters control unit 17. The presence is thenmeasured by pressure gauge 41 and after passing through control valve 44the air flow is measured by flow meter 42. The air then enters airmanifold 43 through coupling 40 to air hose 19 which provides the mainair flow through quartz tube 25 around filament 15.

A tank inlet hose 52 carries air from control unit 58 to tank 48. Asbest seen in FIG. 4, tank inlet hose 52 is connected to dip tube 54which extends below the surface of coating material 55 which is held intank 48. In the preferred embodiment when feed air leaves dip tube 54beneath the surface of coating material 55, the

air bubbles through and vaporizes some coating material. If desired, thefeed air as well as the coating material may be heated to increasevaporization of coating material. After bubbling through coatingmaterial 55, the feed air carrying vaporized coating material leavestank 48 through outlet hose 53 which is connected to feed air manifold45 as best seen in FIG. 3. Feed air carrying vaporized coating liquidthen leaves manifold 45 through feed line 22 which is attached to nozzle14. In nozzle 14, the feed air carrying coating material blends'with themain air flow.

In the preferred embodiment, feed line 22 enters the nozzle 14 at anangle which permits the coating material to enter the air stream in adirection which compliments the flow of air through the nozzle as seenin FIG. 2. Various other methods of introduction are suitable. Thecoating material may for example be introduced into the main air streambefore the air stream passes over the filament. This method ofintroduction is ad- I vantageous in that the coating material becomesmore quartz tube and filament, the temperature of the gas I stream willdrop as low as 300F. Quartz tube 25 is protected by tube shield 26, end56 of which is connected thoroughly blended with the main air or gasstream and the coating material is exposed to a high temperature for alonger period. The method has a disadvantage in that the filament lifebecomes somewhat reduced due to the presence of the material. Some ofthe other methods which have been used to introduce coating materialinto the heated gas stream are nebulizers and devices for introducingdrops of liquid material. The rapid velocity of the heated air has alsobeen used to create a vacuum to suck material into the heated airstream.

In the preferred embodiment shown in FIG. 1, guns 13 are attached toarms 32, 33, 34 and 35 by means of holders 36, 37, 38 and 39. Arms 32and 35 are supported by cross bar 30 and arms 33 and 34 are supported bycross bar 31. Cross bar 30 is held in a horizontal position by upright27 and cross bar 31 is likewise held in a horizontal position by upright28. The lower ends of uprights 27 and 28 are attached to frame 59 whichalso supports conveyor 12.

In operation, the nozzle 14 of guns 13 are directed at container 11.Heater air carrying coating material leaving nozzle 14 inpingescontainer 1 1 and deposits a coating thereon.

Although a four gun unit is shown in FlG. 4, arrangements having greateror fewer guns is suitable. FIG. 5, for example, shows one arrangementfor supporting two guns in a coating position.

Even with a two gun coating unit, better coatings and coatingefficiencies can be obtained with Sn Cl than with any prior art method.In addition, the inventive coating device can effectively andefficiently utilize Ti Cl as the coating material which was not possibleusing prior art methods. For example, two types of hood coaters used inthe prior art and a four gun coating unit and a two gun coating unit inaccordance with this invention were compared. Glass bottles were coatedwith Sn Cl on each of the four coaters and the reflectivity of thecoatings, which is an indication of coating thickness, was compared withthe consumption in pounds per 24 hours of Sn C14 by each unit. Theresults are shown in Table 1.

The table shows that the higher reflectivities result from a coatingmade using the gun units of this invention while less material was used.The higher reflectivities indicate a slightly thicker film.

In addition, the gun units use less than one-half of the compressed airrequired for the vapor-hood type coaters and the initial cost of thegun-type coater is less than one-third of the cost of the vapor-hoodtype coater and maintenance is less costly. The vapor hood type unitsalso show a large built up of coating materials on the inside of thehood; whereas, considerably less build up is encountered in the gun-typecoater.

The vapor-hood type coater requires means for raising the hood if anarticle to be coated becomes blocked in the hood. These blockages aresubstantially more frequent than with the gun coater because it isnecessary for the entry ports which carry the vapors to the hood to beabout two inches from the article to be coated. These close tolerancesdo not provide adequate space for a bottle or other article to freelyleave the hood if it accidentally falls over or becomes misaligned.

If the ports are placed at a distance farther from the article to becoated, efficiency falls off drastically. With the gun coater hereindisclosed much larger distances from the article are permissible and inthe above example, a distance of about four inches between the gun andthe article was maintained. lf desirable, increased distances betweenthe gun and the article can be used and distances of 6 inches or moreare acceptable.

Due to the inefficient utilization of the coating material in the hoodtype coater, more coating material is wasted and large volumes of airare necessary to remove unused vapors from the vapor hood. in addition,these vapors would cause a pollution problem if vented to the atmosphereand it is therefore necessary to scrub the vapors from the air whichcarries them from the hood. This problem is minimized when the flamelessgun coater herein disclosed is used. Because of the substantially higherefficiencies, the quantities of unreacted vapors are sharply reducedthus reducing the quantity of air needed to remove vapors and reducingthe problem of cleaning the air before venting to the atmosphere.

While not wishing to be bound by any particular theory, it is believedthat the inefficiency of the vaporhood type coater is because a largeproportion of the vaporized coating material does not reach the surfaceof the article to be coated. The vapors are introduced at low velocitiesand temperature, linger in the hood and are finally exhausted. Aspreviously discussed, the flameless gun type coater herein discloseddirects the coating material at the article to be coated at asubstantially higher temperature and velocity than the vapor hood typecoater. These higher temperatures and velocities contribute to the highefficiency of the apparatus.

Vapor hood coaters are manufactured so that the coating chamber underthe hood becomes saturated with coating vapor. In order to saturate thecoating chamber with vapor, a plurality of ports for carrying coatingmaterial into the chamber are provided. These ports generally have abouta 1/16 inch diameter and generally at least such ports are provided and200 ports is common. With 100 such ports, 200 cubic feet per hour of drycompressed gas such as air is required to obtain a gas velocity of about25 ft/sec through 1/16 inch ports in a unit having only 100 such portswhereas in the coating unit herein disclosed only 50 cubic feet per hourof dry gas is necessary to obtain a velocity of over 40 feet per secondthrough a nozzle having a V4 inch diameter. In order to approach thisvelocity through the ports, the vapor hood coater would have to use over300 cubic feet per hour of dry gas which is six times the amountrequired to operate the flameless gun coating unit. Such highrequirements for dry compressed air are unacceptable due to heavy loadsor the air dryer and increased problems in cleaning pollutants from theincreased volume of air. It is apparent that two such gun units canoperate on less than one-half the dry compressed gas required for thevapor hood coater. It is believed that, the high velocity from the gununit causes the coating material to impinge the surface of the articleto be coated, thus increasing the chances for reaction of the coatingmaterial with the surface of the article, which in turn contributes toincreased efficiency and permits a greater distance between the gun andarticle than was possible in the vapor hood coater between. the wall andthe article.

As previously mentioned,the dry gas passing through the gun is usuallyheated to initial temperatures in excess of 1,500F, and is generallyabove 300F at the surface of the article. The high temperature reducesthe possibility of thermal shock which could cause stresses and crazing.These high temperatures likewise seem to contribute to the superiorefficiency of the gun unit over the prior art vapor hood type of unit.Table number two indicates the drop in coating thickness on the articleas the temperature of the issuing air is decreased. The temperature ofthe article was maintained at a temperature of about 600F and the gastemperature was measured one-fourth of an inch from the gun nozzle.

TABLE NO. 2

Gas Temperature Coating Thickness I000F 100 A 400F 73 A 70F 65 A Thematerial used was tin tetrachloride. The vapor hood coaters in the priorart did not pre heat the gas such as air which carried the coatingmaterial to the hood. The advantages of heating the air were thereforenot realized.

The coating thicknesses are measured by variations in reflectivitieswhich are correlated to the film thickness. In measuring the coatingthickness, alight source is reflected from the surface of the coatedglass article to a photocell. The current induced in the photocell isthen read on a micro ampere meter. The readings on the micro ammeter arethen correlated to film thickness upon the glass article by using glassarticles having a known coating thickness determined by X-Raydiffraction methods.

Numerous organic and inorganic metallic compounds can be used as coatingmaterial in the gun. For example, almost any compound of a metal whichwill pyrolyze at a temperature below the temperature of the heated gasin the gun can be used. While not wishing to be bound by any particulartheory, it is believed that the pyrolysis of the compound will form anintermediate which is believed to be metal or metal ions which seem to.react upon the surface of the vitreous article to be coated to formmetal objects.

Examples of meta] organic compounds which have been used successfullyare tetra isopropyl titanate and tetrabutyl titanate. Among the moreuseful metal inorganic compounds which have been used for coatingvitreous articles are tin tetrachloride and titanium tetrachloride. Tintetrachloride has been used extensively in coating vitreous surfacesmainly because the reaction rate of tin chloride with ambient humidityis slower than the reaction rate ,of titanium chloride with ambienthumidity, thus problems encountered with hydrolysis product of thecoating material were reduced when tin chloride wasused. Problems causedby hydrolysis product include clogging of equipment, unwanted soliddeposits on the vitreous article, acidic products which caused corrosionand loss of efficiencydue to wasted coating material which entered thehydrolysis reaction. In addition, in prior art coaters, due tohydrolysis, the thickness of a coating formed by using titaniumtetrachloride compared to the thickness of a coating formed by using tintetrachloride fell off rapidly as the distance from the nozzle of thecoater to the article was increased. The rapid decrease in the thicknessof the titanium coating was apparently due to increased hydrolysis ofthe titanium tetrachloride as it traveled the increased distance fromthe nozzle to the article to be coated, consequently titaniumtetrachloride could not be effectively used in higher prior art coaters.Tin chloride also has a high vapor pressure and can'be applied in vaporform at ambient room temperature; whereas, titanium tetrachloride to beeffectively used should be vaporized at a temperature above ambient roomtemperature to compensate for the lower vapor pressure of titaniumtetrachloride.

The use of tin chloride, however, has several serious disadvantageswhich would make titanium coating advantageous if the hydrolysis problemof titanium tetrachloride'could be solved.

Tin forms an electrically conductive film on vitreous surfaces whichincreases problems of corrosion such as pinholing and cap rusting;whereas, a coating formed using titanium reduces or eliminates corrosionproblems.

Titanium tetrachloride is substantially less expensive than tintetrachloride and unused titanium compounds can be more easily removedfrom waste gases such as those passing through the hood over the coaterthus problems in preventing pollution are reduced by using titanium.

it has been discovered that the apparatus herein disclosed can utilizetitanium tetrachloride without hydrolysis problems. It is believed thatthe gun coating apparatus can use titanium tetrachloride withouthydrolysis problems for several reasons. The high velocity through thegun decreases the time for reaction of the titanium compound with waterbetween the time when the compound leaves the gun to the time when thecompound strikes the vitreous article to be coated. The high temperaturein the gun prevents the formation of stable hydrolysis compounds beforethe titanium leaves the gun. As previously discussed the temperature inthe gun is in excess of 1,000F; whereas, the highest gas temperature,other than flame coaters, used in delivering the coating material wasabout 200F.

Flame coaters, as previously discussed, deliver the coating material ata high temperature and velocity but do not alleviate the problem ofhydrolysis of coating compounds such as titanium tetrachloride. Whenflame coaters are used, a usual product of combustion is water vaporwhich will rapidly combine with compounds such as titanium tetrachlorideto form hydrolysis products.

What is claimed is: l. A method for coating a vitreous surfacecomprisheating a high velocity gas stream to a temperature of from about700F to about 1,800F; blending with the hot gas stream a metalliccompound which decomposes at a temperature between about 700 to 1,800F;and impinging a vitreous surface preheated to a temperature of fromabout 400F to about l,800F with the blended gas stream whereby saidcompound becomes decomposed and forms a coating on said surface. 2. Themethod of claim 1 wherein said metallic compound is vaporized-in acarrier gas stream prior to said blending step.

1 1 l2 3. A method for coating surfaces manufactured from about 1,800F.vitreous substances comprising: 4. The method of claim 3 wherein saidair stream is introducing a coating material selected from the heated byan electrical resistance heater.

group consisting of Ti Cl and Sn CL, into a hot air 5. The method ofclaim 3 wherein said coating matestream, said hot air stream being at atemperature 5 rial is introduced into said hot air stream by means of ofbetween 700 and 1,800F; and a feed air stream carrying said coatingmaterial in vapor directing said air stream at said surface, saidsurface form.

being at a temperature of from about 400F to

2. The method of claim 1 wherein said metallic compound is vaporized in a carrier gas stream prior to said blending step.
 3. A method for coating surfaces manufactured from vitreous substances comprising: introducing a coating material selected from the group consisting of Ti Cl4 and Sn Cl4 into a hot air stream, said hot air stream being at a temperature of between 700* and 1,800*F; and directing said air streaM at said surface, said surface being at a temperature of from about 400*F to about 1,800*F.
 4. The method of claim 3 wherein said air stream is heated by an electrical resistance heater.
 5. The method of claim 3 wherein said coating material is introduced into said hot air stream by means of a feed air stream carrying said coating material in vapor form. 